1. Technical Field
The present invention relates to an electronic device, a surface emitting laser (i.e. a vertical cavity surface emitting laser (VCSEL)), a surface emitting laser array, a light source, and an optical module.
2. Related Art
A surface emitting laser having an intra-cavity structure is known as a light source for optical interconnection, as shown in Patent Documents 1 and 2, for example. The intra-cavity structure is a structure in which current is injected into the active layer from inside two reflective mirrors, e.g. DBR (Distributed Bragg Reflector) minors, forming an optical cavity, without passing through the reflective minors in one or both directions.
In the surface emitting laser described in Patent Document 1, a lower DBR minor is formed on a substrate. An n-type contact layer and an active layer are sequentially formed on the lower DBR minor, and an n-side electrode is formed on the n-type contact layer. Furthermore, a p-side electrode is formed on the active layer and an upper DBR mirror is formed above the p-side electrode. The surface emitting laser described in Patent Document 1 has a double intra-cavity structure in which current can be injected into the active layer without passing through either the upper or lower DBR minors. With this intra-cavity structure, the surface emitting laser described in Patent Document 1 can realize a low threshold current and high power efficiency.
In the case of an intra-cavity structure in which the current is injected to the active layer without passing through the lower DBR mirror, the lower DBR minor is usually made of an undoped semiconductor, in order to decrease the parasitic capacitance, for example.    Patent Document 1: U.S. Pat. No. 6,750,071    Patent Document 2: Japanese Patent Application Publication No. 2004-103754    Non-Patent Document 1: S. Sekiguchi, et al., Jpn. J. Appl. Phys., Vol. 36, pp. 2638-2639 (1997)
However, beyond the case of a surface emitting laser, in a case of an electronic device that operates by application of a modulated electrical signal, problems may occur such as a decrease in the cutoff frequency of the electronic device due to the parasitic capacitance and an increase in crosstalk between components which occurs when the electronic device is configured in an array. In particular, cutoff frequencies with high frequency characteristics of 20 GHz or more are desired, and there is a great demand for electronic devices that have decreased parasitic capacitance.